Add test for /admin/whois

I accidentally pushed this to develop and reverted it.

Spec: matrix-org/matrix-spec-proposals#198
Synapse: matrix-org/synapse#418

tests/48admin.pl

@@ -0,0 +1,35 @@
+test "/whois",
+   requires => [ $main::API_CLIENTS[0] ],
+
+   do => sub {
+      my ( $http ) = @_;
+
+      my $user;
+
+      # Register a user, rather than using a fixture, because we want to very
+      # tightly control the actions taken by that user.
+      # Conceivably this API may change based on the number of API calls the
+      # user made, for instance.
+      matrix_register_user( $http )
+      ->then( sub {
+         ( $user ) = @_;
+
+         do_request_json_for( $user,
+            method => "GET",
+            uri    => "/api/v1/admin/whois/".$user->user_id,
+         )
+      })->then( sub {
+         my ( $body ) = @_;
+
+         assert_json_keys( $body, qw( devices user_id ) );
+         assert_eq( $body->{user_id}, $user->user_id, "user_id" );
+         assert_json_list( $body->{devices} );
+         assert_json_keys( $body->{devices}[0], "sessions" );
+         assert_json_list( $body->{devices}[0]{sessions} );
+         assert_json_keys( $body->{devices}[0]{sessions}[0], "connections" );
+         assert_json_list( $body->{devices}[0]{sessions}[0]{connections} );
+         assert_json_keys( $body->{devices}[0]{sessions}[0]{connections}[0], qw( ip last_seen user_agent ) );
+
+         Future->done( 1 );
+      });
+   };